Blade lock screw

ABSTRACT

This disclosure relates to the blade lock that serves to secure the blades to the drum rotor of a compressor in a gas turbine engine that is characterized by its ease of removal upon disassembly. The blade lock consists of two components, a locking member that engages the surface of a shoulder formed in the drum of the drum rotor and a screw threadably engaging a threaded central bore formed in the locking member having a platen engaging the bottom surface of the recess to urge the locking member to bear against the shoulder and where the screw carries three equally spaced longitudinal slots formed around the periphery of the threaded portion of the threads of the screw.

This invention was made under a U.S. Government contract and theGovernment has rights herein.

DESCRIPTION

1. Technical Field

This invention relates to compressor rotors for gas turbine engines andparticularly to the means for securing the compressor blades to the drumof the drum rotor or rotor disk.

2. Background Art

The locking means for securing the blades to the drum rotor of thecompressor of gas turbine engines has over time seized and asexperienced it was virtually impossible to remove without having itdrilled out. This had the propensity to cause damage to the drum rotoror rotor disk should there be an inadvertent slip of the drill bit or ifthe screw put up an inordinate amount of resistance to being removed.

An example of a blade locking assembly is disclosed in U.S. Pat. No.3,721,506 granted to B. J. Anderson on Mar. 20, 1973 and entitled"Split-Nut Blade Lock Assembly". This patent discloses a blade lockwhich includes a split nut that threadably engages a set screw. In spiteof the fact that the nut was split, it also had a tendency to seize overtime and require extraordinary means for its removal.

U.S. Pat. No. 3,930,751 granted to W. A. Straslicka et al on Jan. 6,1976 and entitled "Bucket Locking Mechanism" is another example of ablade locking device. This assembly includes locking means for a rotorthat includes a plurality of blades supported to a rotor disk by fittingthe blades in fir tree slots formed in the disk and utilizing a pin-setscrew assembly to hold the blade in place.

There are a number of patents that show screws that are fabricated withaxial slots extending the length of the threaded portion of the screw.U.S. Pat. No. 4,712,957 granted to W. Edwards et al on Dec. 15, 1987 andentitled "Adhesively Secured Fastener" exemplifies these types ofdevices. Typically, the side slots serve to allow the passage ofadhesive to lock the crew in place or chips or metal slivers that areremoved when screwing the screw in place.

This invention contemplates the combination of the slotted screw and ablade lock member that has proven to be capable of being removed withouthaving to go through the extraordinary removal process heretoforerequired.

DISCLOSURE OF INVENTION

An object of this invention is to provided an improved blade lock forthe blades of a drum rotor used in a gas turbine engine.

A feature of this invention is the slotted screw adapted to fit into alocking member to engage the bottom surface of the recess in the drum ofthe drum rotor to urge the locking member upwardly to bear against thesurface of shoulders formed in the dovetail groove of the drum rotor orrotor disk to hold the blades in place where the slot is accessible atthe top surface of the screw to allow admittance of lubricant topenetrate the threads for ease of removal.

The foregoing and other features of the present invention will becomemore apparent from the following description and accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a developed partial view showing the top view of the assembleddrum rotor of a gas turbine engine,

FIG. 2 is a sectional view taken along lines 2--2 of FIG. 1,

FIG. 3 is a side elevation view of the slotted screw of this invention,

FIG. 4 is a top view of the screw shown in FIG. 1 illustrating one typeof tool receiving slot, and

FIG. 5 is a top view illustrating another tool receiving slot.

BEST MODE FOR CARRYING OUT THE INVENTION

While this invention is described in its preferred embodiment of beingused in a drum rotor for a gas turbine engine it will be appreciated byone skilled in this art that the invention has utility in otherapplications. The invention can best be understood by referring to FIGS.1 and 2 which show a portion of a drum rotor as is typically used in agas turbine engine generally indicated by reference numeral 10supporting a row of axially flow compressor blades 12. As is typical inthese types of installations the root section 14 of blades 12 are fittedinto the circumferential dovetail slot 16 formed in the outer peripheryof the drum 18. Once slid into position in the dovetail groove or slot16, the blades are secured by snap rings 17 and 19 formed incircumferential slots 21 and 23, respectively. The blades then must belocked into place by means that are capable of withstanding thecircumferential component of the aerodynamic loads developed duringengine operation. The locking means must be capable of permitting theassembly and disassembly of blades with relative ease. As mentioned inthe above experience has shown that heretofore locking means have seizedover time requiring extraordinary measures for their removal with aconsequential damage to the surrounding hardware.

According to this invention two locking means generally illustrated byreference numeral 20 serve to prevent circumferential movement of theblades 12 and secure them in place. The locking means includes a wedgemember 22 and a set screw 24. Wedge member 22 is generally cylindricalin shape and includes a central threaded bore 26, a smaller diameterneck section 28 and a wider diameter locking section 30. The set screw24 includes a platen 32, a smaller diameter neck section 34, and athreaded body 36. Installed, the locking means is fitted into thedovetail groove or slot 16 and the upper end of the neck sectionprotrudes through drilled aperture 40 formed in the blade's platform 42.Set screw 24 includes a tool receiving recess 44 formed on the topsurface remote from the platen 32 that can be made to accommodateexisting Allen wrenches or can be splined (as shown as recess 40' inFIG. 5) if additional removing torque is required. To assemble thelocking mechanism the locking member or wedge member is installed in thedovetail groove 16 and the set screw is installed to threadably engagethe threads in the central bore 26. With the use of the tool, the setscrew is torqued down so that the platen 32 bears against the surface 46of the dovetail groove 16 and forces the wider diameter locking section30 of wedge member 22 to engage the shoulder 48 formed in the drum 18.This serves to prevent the blades 12 from moving while being capable ofwithstanding the aerodynamic loads encountered during operation.

As noted and according to this invention the set screw 24 includes threeequally spaced axial grooves 50 extending from the top surface to theneck 34. This serves to allow for the ease of removal during teardownafter considerable operation time of the engine without the necessity ofrelying on extraordinary means for removal as has been experienced inthe past. The axial slots 50 not only help in reducing torquing loadsbut also enhances thread cleaning capability and allows the penetrationof lubrication fluids during teardown.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be appreciated and understood bythose skilled in the art that various changes in form and detail thereofmay be made without departing from the spirit and scope of the claimedinvention.

What is claimed:
 1. For a compressor of a gas turbine engine including adrum rotor having a circumferential dovetail groove for receiving aplurality of compressor blades each having a root portion, platformsadjacent said root portion of said blades, the side edges of saidplatforms abutting adjacent side edges of adjacent platforms, theimprovement comprising:means including a wedge member and a set screwhaving external threads engaging threads formed in a central bore insaid wedge member, a land formed on a first end of the set screw havinga surface engaging the bottom surface of said dovetail groove, a toolaccess recess formed on a second end of said set screw remote from saidland, said set screw having at least one axial slot extending throughsaid external threads from said land to said second end on the side ofsaid set screw, an enlarged diameter portion on said wedge memberficitionally engaging a side surface of said dovetail groove to locksaid blades into position in said dovetail groove, and an opening in atleast one of said side edges of said adjacent platforms affording accessto said tool receiving recess to torque down said set screw and forcesaid wedge member in engagement with said side surface.
 2. For acompressor of a gas turbine engine as claimed in claim 1 wherein saidset screw includes a reduced diameter neck section disposed between saidland and said threads and includes three equally spaced axiallyextending slots extending from the top of said screw to said neckwhereby lubricant can be admitted to said threads.
 3. For a compressoras claimed in claim 2 wherein said recess is splined to accommodate asplined shaped tool.
 4. For a compressor as claimed in claim 2 whereinthe opening in at least one of said side edges of adjacent platforms isdisposed centrally between adjacent platforms.